High conversion of C3 and C4 olefins to corresponding unsaturated aldehydes and acids with stable molybdenum catalysts

ABSTRACT

A stabilized heteropoly molybdate catalyst precursor in calcined form and containing anionic molybdenum in defect state is surface impregnated with certain metal cations. The stabilized precursor is one obtained by incorporating into the reaction product of a molybdate and a soluble phosphate, silicate or arsenate, an aqueous chloride ion and a compound of phosphotungstate, silicotungstate, vanadium arsenate, silico-arsenate, phosphovanadate, or silicovanadate, followed by drying and calcining. During the chloride ion stabilization step other metals may be optionally incorporated in forming the stabilized precursor. 
     The obtained precursor is catalytically active in the conversion of the unsaturated aldehydes to the corresponding unsaturated carboxylic acids with or without incorporation of the metal cation during the chloride ion stabilization step. When the obtained calcined precursor is surface impregnated with a Group VIII metal cation, preferably cobalt and/or iron, and with a compound of selenium or tellurium, the resulting catalysts are highly active and are capable of direct conversion of C 3  -C 4  monoolefins in a single step to the corresponding unsaturated carboxylic acids.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a division of application Ser. No. 133,045, filedMar. 24, 1980, now U.S. Pat. No. 4,272,408, which is acontinuation-in-part of application Ser. No. 952,177, filed Oct. 17,1978, now U.S. Pat. No. 4,212,767.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to methods for the preparation of stableheteropoly molybdate catalysts and use of certain of the obtainedcatalysts particularly in the conversion of C₃ and C₄ olefins to theircorresponding unsaturated aldehydes and unsaturated acids.

2. Description of the Prior Art

The preparation of acrylic acid from propylene and the preparation ofmethacrylic acid from isobutylene are generally carried out in twostages under independently selected conditions for each stage and mostoften employing different catalysts selected for each stage. In thefirst stage the olefin is catalytically oxidized to the aldehyde withthe formation of possibly a small amount of the corresponding C₃ or C₄unsaturated acid. The obtained aldehyde is converted to the acid in thesecond stage generally in the presence of a different catalyst. Amongthe better known commercial processes, the production of acrolein iseffected by catalytic oxidation of propylene with oxygen over supportedCuO catalyst at about 350° C.; or by air oxidation of propylene overBiO₃ /MoO₃ catalyst at 300°-360° C. The oxidation of the acrolein formedby the foregoing or other processes is carried out in a second catalyticreactor generally at a temperature of about 250° C.

Numerous different catalysts have been proposed in the prior patentedart for the conversion of acrolein and methacrolein to the correspondingunsaturated acids, more generally comprising metal molybdates andphosphomolybdates combined with various metal cations. Typical amongsuch are U.S. Pat. Nos. 3,326,817; 3,865,873; 3,875,220; 3,882,047;3,925,464; 3,976,888; 3,998,876; 4,000,088; 4,001,316; 4,017,423;4,025,565; 4,035,262; 4,042,533; 4,042,625; 4,045,478, 4,051,179;4,070,397; 4,072,708; 4,075,123; 4,075,124; and 4,075,244.

As an example of such prior art methods is that described in U.S. Pat.No. 3,965,163. As therein described, a solution of antimony trichloridein hydrochloric acid is combined with phosphomolybdic acid, and tungstentrioxide is then added to the obtained solution. The resulting mixturewhen dried and calcined forms a catalyst having the empirical formula

    Sb.sub.1 Mo.sub.12 W.sub.1 P.sub.1 O.sub.41.5

U.S. Pat. No. 4,034,008 discloses the oxidation of alpha, betaunsaturated monoolefins with molecular oxygen to produce the unsaturatedacid as well as the unsaturated aldehyde. The reaction is carried out inthe presence of steam at about 350°-450° C. over catalyst comprising amajor portion of molybdena associated with oxides of bismuth, iron,silica, nickel or cobalt, antimony or ruthenium and optionallycontaining chloride ion. At best only about 1 to 2 parts by weight ofacrylic acid are obtained along with about 13 to 15 parts acrolein orabout 1 to 2.65 parts acrylic acid with 16 to 19 parts acrolein.

SUMMARY OF THE INVENTION

In the aforesaid parent application Serial No. 952,177 a method isdescribed for preparing molybdate catalysts of high purity andstabilized activity by utilizing a chloride ion stabilization step (CIS)wherein a water-soluble non-metallic molybdate is combined with awater-soluble compound of an element from the group consisting ofsilicon, phosphorus and arsenic in aqueous solution and there is addedto this mixture an aqueous chloride ion and a compound selected from thegroup consisting of phosphotungstate, silicotungstate, vanadiumarsenate, silico-arsenate, phosphovanadate, silicovanadate or mixturesof these. By drying and calcining the resulting reaction product, astable, active oxidation catalyst is obtained having an empiricalformula

    Y.sub.w Mo.sub.x A.sub.y O.sub.z                           (I)

wherein Y is phosphorus, arsenic, silicon or mixtures thereof,

A is tungsten, vanadium, arsenic (when Y is not arsenic), or mixturesthereof,

and w, x, y, and z are numerical quantities defining the relative molarproportion of these elements in the catalyst.

As disclosed in said parent application the activity of such catalystscan be further enhanced by incorporating a metal cation therein duringthe chloride ion stabilization step, resulting in a catalyst of theempirical formula

    X.sub.u Y.sub.w Mo.sub.x A.sub.y O.sub.z                   (II)

wherein Y and A and the common subscripts are the same as in Formula Iabove, and X is one or more of the selected metal cations, and u is anumber indicating the proportionate mole quantity of X present in thecatalyst.

The catalysts prepared in accordance with the methods described in saidprior parent application are advantageously useful in oxidizingunsaturated aldehydes such as acrolein and methacrolein respectively toacrylic and methacrylic acids.

In accordance with the present invention calcined molybdate catalystsprepared by utilizing the CIS step of said prior patent application areemployed as precursors, into the surface of which one or more of certainmetal cations are further incorporated, preferably including among thesea Group VIII base metal. The preferred catalysts of the presentinvention comprise as the metal cation incorporated into the calcinedmolybdate catalyst precursor cobalt and/or iron optionally together witha non-metallic ion from Group VIA (selenium or tellurium). Catalysts ofthe present invention correspond to the empirical formula

    D.sub.1-5 E.sub.0-1 G.sub.0.5-4 P.sub.0.5-3 Mo.sub.10-12 L.sub.0-2 O.sub.z (III)

wherein D can be one or more elements from the group iron, cobalt,nickel, copper, bismuth, chromium, tin, manganese antimony and lead;

E can be an alkaline earth metal such as magnesium, barium or strontium;

G can be silicon, tellurium, selenium or arsenic;

L is one or more elements from the group consisting of tungsten andvanadium, and

z is the residual valence to satisfy the formula.

When the proportion of D is increased to above 3 and up to about 6, highyields of aldehyde are obtained in the conversion of olefins.

The preferred catalysts of the invention are those which are active inthe one-step oxidative conversion of C₃ and C₄ monoolefins obtaininghigh yields of oxidized products including the corresponding unsaturatedmonocarboxylic acids as well as the corresponding unsaturated aldehydes.These preferred catalysts correspond to one of the empirical formulae

    M.sub.2.3-5 R.sub.2-3 P.sub.1.5-2.5 Mo.sub.20 O.sub.z      (IV)

    M.sub.1-3 R.sub.0.5-2 P.sub.1-1.5 W.sub.1-2 Mo.sub.10 O.sub.z (V)

    M.sub.1-2 R.sub.1-3 P.sub.2-4 W.sub.1-3 Mo.sub.20 O.sub.z  (VI)

wherein M comprises one or more metal cations, at least one of which isa base metal cation from Group VIII of the Periodic Table and preferablycobalt, iron or both of these,

and R is at least one element from the group consisting of selenium andtellurium. The preferred catalysts of formulae IV, V, VI, are those inwhich the ratio of metal cation (M) to molybdenum is not more than about3/10. With increase in proportion of metal cation highly activecatalysts are obtained for conversion of olefins to unsaturatedaldehydes but such catalysts lose activity and selectivity for directone-step conversion of the olefin to the corresponding unsaturatedcarboxylic acid.

In the above formulae IV to VI part of the phosphorus may be replaced bysilicon, arsenic or boron; the total content of phosphorus and suchreplacement falling within the indicated proportions. Also the tungstenin formuale V and VI may be partly replaced by vanadium.

DETAILED DESCRIPTION Preparation of the Precursor

The precursors employed in preparing the final catalysts of the presentinvention are prepared employing the chloride ion stabilization step asdescribed in aforesaid parent application Ser. No. 952,177. By utilizingsuch stabilization step, the need for precise pH control during thecrucial stages of the preparation is avoided, and the obtainedprecursors themselves have high catalytic activity in oxidation ofaldehydes to corresponding acids even without incorporation of metalcations.

In preparing the precursors following the method of the aforesaid priorpatent application, a molybdic acid or soluble non-metallic molybdate iscombined with a water-soluble acid or non-metallic salt of an elementselected from the group consisting of silicon, phosphorus and arsenic inaqueous solution, and then there are added to the mixture an aqueouschloride ion and a compound selected from the group consisting ofphosphotungstate, silicotungstate, vanadium arsenate, silico-arsenate,phosphovanadate, silicovanadate, corresponding acids thereof or mixturesthereof. The resulting combination is dried and calcined to yield theprecursor product having an empirical formula

    Y.sub.w Mo.sub.x A.sub.y O.sub.z                           (I)

wherein Y is phosphorus, arsenic, silicon or mixtures thereof,

A is tungsten, vanadium, arsenic (when Y is not arsenic), or mixturesthereof,

w ranges from 0.5 to 1.5

x ranges from 10 to 15

y ranges from 0.1 to 2.0 and

z is an integer necessary to satisfy the valency requirements of theformula, ranging from 1 to 42.

Higher catalytic activity is imparted to the precursor products if oneor more metallic cations are incorporated during the chloride ionstabilization step. Such metallic cation can be selected from the groupconsisting of aluminum, antimony, barium, bismuth, cadmium, calcium,cerium, chromium, cobalt, copper, iron, lanthanum and other rare earths,lead, magnesium, manganese, nickel, potassium, rhenium, rhodium,ruthenium, silver, strontium, thallium, titanium, zinc, zirconium, andmixtures thereof.

The non-metallic molybdate salts used in the catalyst precursorpreparation include ammonium molybdate [(NH₄)₂ MoO₄ ] and ammoniumheptamolybdate [(NH₄)₆ Mo₇ O₂₄.4H₂ O], molybdic acid, molybdic oxide andmolybdenum trioxide. For the preparation of precursors containingcations in addition to the molybdates salts referred to above, anymetallic molybdate can be used such as barium molybdate, calciummolybdate, iron molybdate, lead molybdate, potassium molybdate andstrontium molybdate. It is critical when the metallic molybdate saltsare employed that the final precursor has a total metal cation tomolybdenum ratio in the range of about 1:10 to about 1:13.

The compound of silicon, phosphorus or arsenic for the preparation ofthe precursor can be an acid or a non-metallic silicate, phosphate orarsenate such as ammonium silicate, ammonium phosphate, ammoniumarsenate, phosphoric acid, orthoarsenic acid, metaarsenic acid,pyroarsenic acid, arsenous oxide, arsenous hydride, hypophosphoric acid,metaphosphoric acid, orthophosphoric acid, pyrophosphoric acid,hypophosphorous acid, orthophosphorous acid, and pyrophosphorous acid.

The chloride ion stabilization (CIS) step takes place in the presence ofconcentrated hydrochloric acid or other material such as an aqueoussolution of ammonium chloride having a high concentration of chlorideions at temperatures in the range of 20° to 80° C. In the case of themetal cation-containing precursor, all or a part of the chloride ion cancome from the chloride of one or more of the cations incorporated intothe catalyst during this CIS step.

The presence of the chloride ion is critical for the uniform formationof the active molybdenum species and to avoid the conflicting influencethat pH tends to have on the aqueous solution during the method ofpreparing the precursor. The preferred results are obtained when thechloride ion is present in the CIS step in the ratio of one equivalentof chloride ion to one equivalent of molybdenum, but the chloride canrange in concentration as high as five equivalents per equivalent ofmolybdenum. Although most, if not all of the optional metal cation isincorporated into the precursor during the CIS step, the cations canalso be added with the molybdate salts as discussed above.

A suitable form of the metal cation that can be incorporated into theprecursor if desired, includes the halides, oxides, nitrates, ammoniumsalts, hydroxides, acetates, carbonates, sulfates and the like. Aparticularly useful form is the chloride of Al, Sb, Ba, Bi, Cd, Ca, Ce,Cr, Co, Cu, Fe, La, Pb, Mg, Mn, Ni, Nd, K, Pr, Re, Rh, Ag, Sr, Tl, Ti,Zn, Zr, and mixtures thereof. The total metal cation to molybdenum ratioshould be in the range of 1 mole cation to about 10 gram atomsmolybdenum to 1 mole cation to about 13 gram atoms molybdenum.

The empirical formula for the precursor containing the metal cation is

    X.sub.u Y.sub.w Mo.sub.x A.sub.y O.sub.z

wherein X is one of the metal cations listed above, or mixtures ofthese;

u ranges from 0.5 to 2.0; and

Y, A, w, x, y and z are the same as that set forth above in formula (I).

The tungsten, vanadium, arsenic, or mixtures of elements are present inthe precursor, preferably so that the mole ratio is 0.25 to 2.0 moles toabout 12 moles molybdenum. The best results are obtained where theelements are incorporated into the catalyst in an aqueous solution ofphosphotungstate, phosphotungstic acid or similar heteropolyanion-containing compounds.

When the CIS step is not followed or when the raw materials exceed themole limits given, inactive molybdenum species are formed in solution.It has been found that when the chloride ion is not present, themolybdenum species may exist in solution in different inactive formsrather than being present as the active molybdate anion. The presence ofchloride ion also maintains the molybdenum species in a very highlycomplexed form, which is the active species. For example, the additionof the preferred phosphorus element creates the active phosphomolybdateanion in solution, and the chloride ion stabilizes this anion during theremaining steps of the precursor preparation. The most preferred resultsare obtained when molybdenum is present as the 12-phosphomolybdateanion. However, similar results are obtained from isomorphous heteropolysilicomolybdates, arseno molybdates or mixtures thereof.

The foregoing method of preparation using the ratios of the rawmaterials set forth above prevents the formation of other molybdenumspecies which are structurally different and not active for theoxidation of carboxylic aldehydes to the acids. This method alsoprevents the formation of inactive molybdenum trioxide species duringthe drying and calcination steps, and thereby gives the highly pure andsubstantially active molybdenum species. By maintaining the structuralpurity, one obtains as precursor an excellent initial catalyst withimproved activity, selectivity and stability.

The addition of the optional metal cations in the ratio set forth abovealso prevents the formation of less selective regular molybdates, andalso results in the elimination of excess metal oxides in the catalyst.In either case, the formation of precursors and catalysts having lowstability is avoided.

The prior art shows that the molybdenum compounds and other metal oxidestend to catalyze reactants to total combustion and to form oxygenatedproducts which tend to decrease the selectivity to, for example, acrylicand methacrylic acids and to decrease the structural stability of thecatalysts. Therefore, the formation of metal oxides and such molybdenumcompounds must be avoided.

Preferably, phosphotungstic acid is employed in the formation of theprecursors prepared by the described method in the ratio 0.5-1.0 molesper mole of molybdenum to form the isomorphous phosphotungsto molybdateanion. Using these small ratios, the phosphotungstic acid helps to formthe most active distorted phosphomolybdate anion having a very stablestructure and a structure which is resistant to deterioration.

After the chloride ion stabilization step, the resulting mixture isdried at temperatures of 75° to 150° C., and the dried product iscalcined in air at temperatures from 150° to 500° C., preferably 200° to420° C. for a period of 1 to 48 hours. The calcined product can then beground to increase its surface area to a range of 35 to 100 mesh havinga surface area of 0.1 to 50 m² /g.

If desired, the catalyst precursor can be supported on any known carriersuch as silica, alumina, Alundum, zeolites, graphite, pumice, siliconcarbide, zirconia, titania or other inert carrier. The precursorproducts used in the method of the present invention can be coated ontoor otherwise incorporated in the carrier in the range of about 10 to100% by weight based on the weight of the carrier. This can beaccomplished by any of the various means well-known to those skilled inthe art.

The precursors of the present invention can be used as catalysts tooxidize unsaturated aldehydes such as acrolein and methacrolein in thepresence of molecular oxygen to yield acrylic acid and methacrylic acid,respectively. The oxygen may be in the form of pure oxygen, oxygendiluted with inert gases, air with or without additional oxygen. Theoxidation reaction can be in either a fixed or fluidized catalyst bed attemperatures in the range of 200° to 475° C., preferably from 250° to375° C., pressures from 0.5 to 50 atmospheres, preferably 1 to 10atmospheres absolute. The residence time of the reactants in thepresence of such catalyst ranges from 0.2 to 30 seconds, preferably 1 to20 seconds. The ratio of oxygen to unsaturated aldehydes in the feed gasranges from 1:1 to 10:1, preferably from 1:1 to 3.1.

Preferably, steam is added to the gaseous reaction mixture to improvethe yield of unsaturated carboxylic acids from the aldehydes. Helium,nitrogen, saturated hydrocarbons such as methane, propane, butane or thelike, or other inert gases can also be added to the gaseous reactantmixture. The concentration of steam ranges from 2 to 80%, preferablyfrom 10 to 50% of the volume of the feed.

In addition to the production of unsaturated carboxylic acids, theprecursors can also be employed in the oxidation of unsaturatedmonoolefins such as propylene and isobutylene to the correspondingunsaturated acid and/or aldehydes such as acrylic and methacrylic acidand acrolein and methacrolein. A preferred reaction mixture for theoxidation of monoolefins comprises one mole of olefin to 1.5 to 3 molesof molecular oxygen and 0.5 to 20 moles of water in the form of steam.The reaction takes place at temperatures in the range of 300° to 500°C., preferably 360° to 450° C., 1 to 10 atmospheres, preferably 1 to 2atmospheres absolute and a residence time of 0.1 to 10, preferably about0.5 to 3 seconds.

The method for preparation of the described precursors can also beextended to prepare other molybdate catalysts which are useful in a widevariety of other chemical processes including dehydrogenation,ammoxidation and dehydrocyclization.

The following examples illustrate embodiments for preparation ofprecursors useful in practice of the present invention. It is to beunderstood, however, that these are for illustrative purposes only andare not intended to be wholly definitive as to the operating conditionsand scope for the preferred practice of the methods of the presentinvention.

EXAMPLE 1

A quantity of 210.0 grams of ammonium molybdate was dissolved in 600 ml.of water. 13.2 grams of diammonium phosphate were dissolved in 100 ml.of water and then added to the ammonium molybdate solution. During thechloride ion stabilization (CIS) step, 25 cc of concentratedhydrochloric acid and 20 grams of phosphotungstic acid dissolved in 15ml. of water were added to the aqueous solution of reactants. Themixture was then dried at 85° C. and calcined at 350° C. for 6 hours.Under these conditions, the resulting composition was found to beessentially free of chloride ion by elemental analysis. The presence ofthe chloride ion is believed to be detrimental to the catalyst activity.

The resulting precursor product had an empirical formula as follows:

    P.sub.1.09 Mo.sub.12 W.sub.0.9 O.sub.z

where z is an integer to meet the valency requirements of the formula.

The precursor material was then ground to a uniform particle size in therange of from about 500 to 600 microns. The precursor was subjected toinfrared spectroscopy, X-ray diffraction and surface aciditymeasurements. From these characterization methods, it was confirmed thatthe active component therein is a distorted phosphomolybdate anion. Inaddition, it was confirmed that no other molybdates or molybdenumtrioxide compounds were present.

To test catalytic activity of the obtained precursor it was placed in afixed bed, stainless steel reactor 18 inches (46 cm.) in length and 5/8inch (1.65 cm.) inside diameter. The reactor was inserted to a length of12 inches (30 cm.) in a heated zone to convert methacrolein tomethacrylic acid under the following reaction conditions to achieve thefollowing results:

    ______________________________________                                        Feed:  Methacrolein                                                                             Oxygen      Steam Helium                                           4.1%       8.35%       12.5% 75.0%*                                    Temperature:  320° C.                                                  Pressure:  Atmospheric                                                        Residence Time:  1.32 seconds                                                 Space Velocity:  2730 hr..sup.-1                                               ##STR1##                                                                     Selectivity of Methacrylic Acid, mole %:                                       ##STR2##                                                                     Selectivity of Acetic Acid, mole %:                                            ##STR3##                                                                     ______________________________________                                         *By volume                                                               

EXAMPLE 2

The catalyst preparation procedure of Example 1 was followed to yield acatalyst precursor having the following structural formula:

    P.sub.1.12 Mo.sub.12 W.sub.1.2 O.sub.z

This product was tested under exactly the same oxidation conditions asthe product of Example 1. The resulting conversion to methacrylic acidwas 83.3% and the selectivity of methacrylic acid was 87.2% and ofacetic acid was 9.2%.

EXAMPLE 3

The Example 1 product preparation procedure was again followed to yielda product having the following formula:

    P.sub.1.18 Mo.sub.12.0 W.sub.1.8 O.sub.z

This product was tested under the same conditions that were followed inExample 1 to produce methacrylic acid. The precursor product showed an80.1% conversion and a selectivity of methacrylic acid equal to 82.7%,and of acetic acid equal to 12.1%.

The foregoing data of Examples 1-3 illustrates that even without theaddition of a metal cation during the formation of the precursor theoxidation activity was very high even when compared to prior artcatalysts which contain one or more metal cations.

EXAMPLE 4

The procedure of Example 1 was generally followed except that the CISstep was varied to illustrate the improvement one can make in thealready high activity of the precursors by the incorporation of at leastone metal cation.

During the CIS step, 22.6 grams of antimony trichloride were dissolvedin 6 cc of concentrated hydrochloric acid and diluted with 20 cc water.This solution was added to the aqueous solution resulting from acombination of the ammonium molybdate and diammonium phosphate. 15 gramsof phosphotungstic acid dissolved in 50 ml. water were then added to themixture and the slurry was dried to 85° C. and calcined at 350° C. for 6hours. The empirical formula of the product is set forth in Table Ibelow.

After the precursor was ground to reduce the size to about 560 microns,the oxidation reaction of Example 1 was followed to convert methacroleinto methacrylic acid except that the temperature was lowered from 320° C.to 304° C. and the residence time was increased from 1.32 to 3 seconds(1200 hr.⁻¹ space velocity). The conversion was 89.0% with a selectivityof methacrylic acid equal to 96.2% and of acetic acid equal to only0.98%.

EXAMPLE 5

The procedure of Example 4 was followed except that during the CIS stepin place of the 22.6 grams of antimony trichloride were added a mixtureof 26.1 grams of lead nitrate and 6.5 grams of cobalt nitrate. Theresulting product was reacted under the same oxidation conditions ofExample 4 to achieve the results set forth in Table I below.

EXAMPLE 6

The procedure of Example 4 was generally followed except for thefollowing modifications. During the CIS step, 14.5 grams of lead nitrateand 7.5 grams of cobalt nitrate were dissolved in 6 cc of concentratedhydrochloric acid and diluted with 20 cc water. 30 grams ofphosphotungstic acid dissolved in 50 ml. water were added to the mixtureof lead nitrate, cobalt nitrate, ammonium molybdate and diammoniumphosphate already combined and in solution. The results of this productwhen tested as catalyst in the oxidation of methacrolein under theExample 4 conditions are also given in Table I below.

EXAMPLE 7

The procedure of Example 6 was followed except that in place of the 14.5grams of lead nitrate and 7.5 grams of cobalt nitrate were added, 7.5grams of barium nitrate, 8.3 grams of lead nitrate, 3.5 grams of cobaltnitrate and 7.5 grams of strontium nitrate. The results of the use ofthis product as catalyst in the oxidation of methacrolein under theExample 4 conditions are set forth in Table I below.

In all of the procedures described in Examples 4-7, the metal cation tomolybdenum ratio was 1:12.

CONTROL 1

A control catalyst was prepared using the procedure of Example 4 exceptthat the step of incorporating 20 grams of phosphotungstic acid waseliminated. The catalyst was employed in the oxidation of methacroleinusing the same conditions as Example 4. The results are also given inTable I below.

                                      TABLE I                                     __________________________________________________________________________                              SELECTIVITY                                                                   METHACRYLIC                                                                             ACETIC                                           PRODUCT       CONV.                                                                              ACID      ACID                                      __________________________________________________________________________    EXAMPLE                                                                       4      Sb.sub.1 P.sub.1.09 Mo.sub.12 W.sub.0.9 O.sub.z                                             89.0%                                                                              96.2%      0.981%                                   5      Co.sub.0.21 Pb.sub.0.78 P.sub.1.09 Mo.sub.12 W.sub.0.9 O.sub.z                              76.4%                                                                              77.4%     8.0%                                      6      Co.sub.0.5 Pb.sub.0.5 P.sub.1.18 Mo.sub.12 W.sub.1.18 O.sub.z                               64.2%                                                                              95.1%     1.0%                                      7      Ba.sub.0.25 Co.sub.0.25 Sr.sub.0.25 Pb.sub.0.25 P.sub.1.18                    Mo.sub.12 W.sub.1.18 O.sub.z                                                                60.7%                                                                              90.1%     1.5%                                      CONTROL                                                                       1      Sb.sub.1 P.sub.1 Mo.sub.12 O.sub.z                                                          36.8%                                                                              Trace     Nil                                       __________________________________________________________________________

Table 1 above illustrates the unexpected results one obtains from thecatalyst precursors employed in the method of the present inventionwhich contain the defect heteropoly phosphomolybdate anion compared tothe results one obtains from a catalyst containing antimonyphosphomolybdate of the type described in the prior art, for example,U.S. Pat. No. 3,965,163. The foregoing results also indicate that themajor significant active species in the precursor product employed inmaking the catalysts of the present invention, is this defect heteropolyphosphomolybdate anion. One is not restricted to the incorporation ofany metal cation or any particular composition in the method ofpreparation of such precursors.

CONTROL 2

A second control catalyst was prepared using the procedure of Example 1except that no hydrochloric acid or other chloride ion-containing mediumwas used in the catalyst preparation to obtain a catalyst having thesame empirical formula as the product of Example 1, i.e.: P₁.09 Mo₁₂W₀.9 O_(z).

Under the identical oxidation conditions, as described in Example 1, noappreciable reaction of methacrolein to methacrylic acid was observed.The oxidation temperature was then increased to 345° C. Under theseconditions, the conversion was 61.7%, and a selectivity of methacrylicacid equal to 45.6% and of acetic acid equal to 17.5% were obtained.

The second control catalyst was subjected to the same characterizationmethods as the product of Example 1 and showed the presence ofconsiderable amounts of molybdenum trioxide along with phosphomolybdate.This is believed to be the cause for the poor activity of this controlcatalyst.

EXAMPLE 8

This example illustrates the unique properties of the CIS methodemployed in producing a precursor of high activity for oxidizingacrolein to acrylic acid under the identical conditions described inExample 4. The conversion of acrolein to acrylic acid using the same Sb₁P₁.09 Mo₁₂ W₀.9 O_(z) catalyst of Example 4 was 89.6% conversion and aselectivity of acrylic acid equal to 88.8% and of acetic acid equal to6.2% were obtained.

The foregoing examples clearly illustrate the extraordinarycharacteristics of these products which contain the essentially pure andstable phosphomolybdate anion as determined by their activity inoxidizing unsaturated aldehydes to the corresponding carboxylic acids.

PREFERRED EMBODIMENTS OF THE PRESENT INVENTIONS

The starting material for preparation of the highly active and selectivecatalysts of the present invention is a stable heteropoly molybdateprecursor corresponding to formula I or II above and prepared by themethod above described employing the chloride ion stabilization step.The precursor is employed in already calcined form and furtherimpregnated and treated as hereinafter described.

To obtain the highly active catalysts useful in the conversion of C₃ andC₄ olefins in a single stage directly to the corresponding unsaturatedcarboxylic acids, the precursor is treated to incorporate apredetermined amount of one or more Group VIII base metals and with aselenium or tellurium compound, then dried and calcined. The resultingfinal catalyst has the empirical formula corresponding to one of theformulae IV, V, or VI above.

The starting heteropoly molybdate precursor employed must contain themolybdenum in a well defined defect structure. The subsequentimpregnation with the metal cation must be kept within limiting rangesto obtain catalysts capable of forming desired amounts (5% or more) ofunsaturated acid directly from the olefin. As the amount of incorporatedcation is increased, above about 3 moles per 10-12 moles of molybdenum,the yield of unsaturated acid formation from the olefin is decreased andhigher aldehyde formation is favored.

Catalysts of substantially the same empirical formula and compositionprepared by techniques other than that employed in accordance with thepresent invention, do not demonstrate the high activity and selectivityas the catalysts of the invention. X-ray analysis of sample catalysts ofthe invention show the molybdenum to be present as the defectphosphomolybdate anion, while catalysts of the same composition preparedby other methods are found to contain a mixture of different molybdenumspecies, in which the molybdenum is tetrahedrally and octahedrallysurrounded as regular molybdates. Such regular molybdate containingcatalysts are less active and less selective in various selectiveoxidation reactions, than the catalysts made in accordance with thepresent invention. In addition, catalysts prepared in accordance withthe invention have greater structural purity, as identified andconfirmed by infra-red and X-ray investigations, than hitherto knowncatalysts. The unusual catalytic properties of the novel catalysts ofthis invention are believed to result from the fact that the molybdenais present in the heteropoly phosphomolybdate anion state which is mucheasier to reduce.

Catalysts prepared by the method of the present invention have certaincommon physical and chemical properties. They have typical infra-redbands at 800 cm⁻¹, 970 cm⁻¹, 1070 cm⁻¹ and 1400 cm⁻¹. Their X-raypatterns are substantially identical as well as their surface areas.

Once the primary matrix of the molybdena in the precursor is fixed byfollowing the chloride ion stabilization method, various improvedmolybdenum catalysts for known petrochemical processes can be preparedtherefrom by the described impregnation technique. Thus, catalystsshowing excellent performance in conversion of methanol to formaldehydeare obtained by impregnating a preformed primary phosphomolybdateprecursor with iron nitrate alone. By impregnating such primaryphosphomolybdate precursor with either bismuth nitrate alone or cobaltnitrate alone, catalysts are obtained which show excellent performancein the conversion of olefins to the corresponding aldehydes or nitriles.

Catalysts of the general formulae IV to X can also be employed in theconversion of ethyl benzene to styrene, conversion of butene to maleicanhydride, direct oxidation of xylenes to carboxylic acids. The unusualactivity of the catalysts is already observed in their ability toproduce high yields of acrolein from propylene even in the absence ofbismuth therein; the presence of bismuth being reported as essential incertain prior art catalysts designated for use in such conversion ofpropylene.

In addition to their advantageous use in conversion of olefins tounsaturated carboxylic acids, the catalysts of formulas IV, V and VIfind use in the conversion of alcohols to the corresponding aldehydes oracids, the preparation of oxo compounds from the corresponding olefins,and the production of nitriles from the corresponding olefins.

EXAMPLE 9 (a) Formation of Catalyst Precursor Ti₂ P₂ Mo₂₀ W₂.4 O_(z)

354 grams of ammonium molybdate are dissolved in 600 ml water containing23.0 grams of mono-basic ammonium phosphate. To this solution there isadded 20 cc of concentrated hydrochloric acid along with 20.0 ml oftitanium chloride. To the obtained mixture there is then added 60.0grams of ammonium metatungstate and the obtained mixture dried withconstant stirring, then calcined at 350° C. for 6 hours.

(b) Preparation of Catalyst Co₁.7 Fe₀.37 Te₃.1 Ti₂ P₂ Mo₂₀ W₂.4 O_(z)

50.0 grams of cobalt nitrate, 15.0 grams of iron nitrate and 48.0 gramsof tellurium dioxide are added to 150 ml water and then mixed with theprecursor (a) above. The obtained product is dried at 120° C. for 6hours, followed by calcination at 350° C. for 6 hours.

EXAMPLE 10 (a) Formation of Catalyst Precursor P₁.6 Mo₂₀ O_(z)

177 grams of ammonium molybdate and 9.5 grams of mono-basic ammoniumphosphate are dissolved in 400 ml water. To this solution there is added20 cc of concentrated hydrochloric acid and the obtained product driedwith constant stirring, then calcined at 350° C. for six hours.

(b) Preparation of Catalyst Co₂.0 Se₂.0 Fe₀.6 P₁.6 Mo₂₀ O_(z)

A solution of 29.1 grams of cobalt nitrate, 12.0 grams of iron nitrateand 12.90 grams of selenious acid in 100 ml water, is mixed with theabove precursor (a) and dried at 120° C. for 6 hours, then calcined at350° C. for 6 hours.

(c) Preparation of Catalyst Co₂.0 Te₃.0 Fe₀.3 P₁.6 Mo₂₀ O_(z)

29.1 grams of cobalt nitrate, 6.0 grams iron nitrate and 24.0 grams oftellurium dioxide are added to 120 ml water, and mixed with the aboveprecursor (a). The mixture is dried at 120° C. for 6 hours, followed bycalcination at 350° C. for 6 hours.

EXAMPLE 11 (a) Formation of Catalyst Precursor Si₁ P₁ Mo₁₀ W₁.0 O_(z)

By the procedure outlined in Example 10(a) above there are combined:

    ______________________________________                                                            Grams                                                     ______________________________________                                        Ammonium molybdate    177                                                     Mono basic ammonium phosphate                                                                       11.5                                                    Silicic acid          12.0                                                    Ammonium metatungstate                                                                              25.0                                                    ______________________________________                                    

followed by drying and calcining as before.

(b) Preparation of Catalyst Co₁.0 Te₁.0 Fe₀.2 Si₁ P₁ Mo₁₀ W₁.0 O_(z)

The above precursor (a) is admixed with an aqueous solution comprising:

    ______________________________________                                                       Grams                                                          ______________________________________                                        Cobalt nitrate   29.1                                                         Iron nitrate     8.0                                                          Tellurium dioxide                                                                              16.0                                                         ______________________________________                                    

in 120 ml water; and the mixture dried and calcined as set out inExample 10(b).

EXAMPLE 12 (a) Formation of Catalyst Precursor Sb₀.5 P₀.55 Mo₉.7 W₀.5O_(z)

By the same procedure set out in Examples 10 and 11 above, there iscombined:

    ______________________________________                                                          Grams                                                       ______________________________________                                        Ammonium molybdate  171.0                                                     dissolved in 400 ml water                                                     Diammonium phosphate                                                                              6.6                                                       Antimony trichloride in                                                                           11.3                                                      20 cc conc. hydrochloric acid                                                 Phosphotungstic acid                                                                              10.0                                                      in 20.0 ml water                                                              ______________________________________                                    

followed by drying and calcining as before.

(b) Preparation of Catalyst Bi₅.0 Fe₂.87 Sb₀.5 P₀.55 Mo₉.7 W₀.5 O_(z)

The dried and calcined precursor of (a) above is added to a solution of:

    ______________________________________                                                           Grams                                                      ______________________________________                                        Bismuth nitrate      242.0                                                    dissolved in 50 ml conc. HNO.sub.3                                            Iron nitrate         115.0                                                    dissolved in 50 ml water                                                      ______________________________________                                    

The product is dried and calcined as in previous example 11(b).

EXAMPLE 13 (a) Formation of Catalyst Precursor P₁.1 Mo₁₂.0 W₁.0 O_(z)

Following the procedures of Examples 10(a) to 12(a) above, a dried andcalcined product is prepared from:

    ______________________________________                                                          Grams                                                       ______________________________________                                        Ammonium molybdate  212                                                       dissolved in 400 cc water                                                     Diammonium phosphate                                                                              6.6                                                       dissolved in 20 cc conc. HCl                                                  Phosphotungstic acid                                                                              20                                                        ______________________________________                                    

followed by drying and calcining.

(b) Preparation of Catalyst Co₅.0 Fe₀.5 P₁.1 Mo₁₂.0 W₁.0 O_(z)

The calcined precursor (a) above is admixed with a solution in 200 mlwater of:

    ______________________________________                                                      Grams                                                           ______________________________________                                               Cobalt nitrate                                                                         145.5                                                                Iron nitrate                                                                            20.2                                                         ______________________________________                                    

and the obtained product dried and calcined as in Examples 10(b) to12(b) above.

Catalysts of Examples 9(b) through 13(b) tested in conversion ofpropylene under the following reaction conditions:

    ______________________________________                                                  Propylene Oxygen     Steam Helium                                   Feed (vol %)                                                                            5.9       13.1       11.0  70.0                                     GHSV at room temperature  1350                                                obtain results shown in Table 1 below compared to                             control catalysts.                                                             ##STR4##                                                                      ##STR5##                                                                     ______________________________________                                    

                  TABLE 1                                                         ______________________________________                                                    SELECTIVITY                                                                 Temp    Conv.   Acrylic                                                                              Acrolein                                                                             Acetic                                Catalyst  °C.                                                                            %       Acid % %      Acid %                                ______________________________________                                        Example 9(b)                                                                            416     98.5    18.9   44.77  6.2                                   Example 10(b)                                                                           400     71.6    5.9    40.74  7.78                                  Example 10(c)                                                                           433     86.7    26.09  68.12  1.52                                  Example 11(b)                                                                           450     71.7    37.23  48.8   3.20                                  Example 12(b)                                                                           400     76.5    1.21   76.28  --                                    Example 13(b)                                                                           400     92.5    Trace  94.21  --                                    Control 3 425     25.1    1.21   40.50  --                                    Control 4 430     36.2    1.7    40.1   --                                    ______________________________________                                    

Among examples of other catalysts of the empirical formulae IV, V, VI,which are prepared by the methods of Examples 9 to 11, and which areuseful in conversion of C₃ and C₄ monoolefins, are:

    Sn.sub.2 Fe.sub.1 Te.sub.0.5 P.sub.1 Mo.sub.10 W.sub.1 O.sub.z (VII)

    Mn.sub.2 Fe.sub.1 Te.sub.0.5 P.sub.1 Mo.sub.10 W.sub.1 O.sub.z (VIII)

    Co.sub.1 Mn.sub.1 Fe.sub.1 Mg.sub.0.5 Te.sub.0.5 P.sub.1 Mo.sub.10 W.sub.1 O.sub.z                                                   (IX)

    Co.sub.2 Fe.sub.0.5 Mg.sub.0.5 Te.sub.1 P.sub.0.5 Si.sub.0.5 Mo.sub.10 W.sub.1 O.sub.z                                           (X)

For the preparation of a control catalyst, the chloride ionstabilization technique (CIS) was not employed. The resulting catalystobtained considerably lower total conversion of propylene and producedonly very small amounts of acrylic acid even at higher temperatures thanneed be employed for the preferred catalysts prepared from precursorsobtained with the CIS technique.

EXAMPLE 14 Preparation of Control Catalyst Mn₂ Bi₁.0 Fe₁.0 Sb₁.0 Co₀.8P₁ Mo₁₂ O_(z)

To a solution comprising 106 grams ammonium molybdate and 5.8 gramsmonobasic ammonium phosphate, there was added: 90.0 grams of cobaltnitrate in 150 ml water; 11.3 grams antimony trichloride in 10 ccconcentrated hydrochloric acid; 24.0 grams of bismuth nitrate in 5 ccconcentrated nitric acid and 20 cc water; 20.0 grams manganese chloridein 20 cc water and a slurry of precipitated iron hydroxide from 20.0grams of iron nitrate. Drying and calcining was as in previous Example10(b).

The infrared spectrum (I.R.) of the above catalyst showed the presenceof typical heteropoly phosphomolybdate anion, as an admixture of regularmolybdates. Hence there was no stabilization of the active heteropolyphosphomolybdate structure. By the regular hitherto known methods only amixture of regular metal molybdates are obtained which are less activeand less selective than the catalytic products obtained in accordancewith the present invention. The poorer activity of such catalysts inconversion of propylene are observed from Table 1 above.

EXAMPLE 15 Preparation of Control Catalyst Bi₅.0 Fe₂.87 Sb₀.5 P₀.5 Mo₉.7W₀.5 O_(z)

This catalyst was prepared using the same amount of the chemicals as inpreparation of the catalyst of Example 12(b), but not using the chlorideion stabilization technique. The method employed was as follows:

To 171.0 grams of ammonium molybdate dissolved in 400 ml water there wasadded 6.6 grams of diammonium phosphate. The obtained solution wasadmixed with a composition prepared from:

242.0 grams of bismuth nitrate in 50 cc concentrated nitric acid and 60cc concentrated hydrochloric acid in 300 ml water;

115.0 grams ferric nitrate dissolved in 400 ml water and precipitated asiron hydroxide by reaction with ammonium hydroxide;

11.3 grams of antimony trichloride in 10 cc concentrated hydrochloricacid; and

10.0 grams of phosphotungstic acid dissolved in 20 ml water.

The obtained slurry was dried and calcined as in previous Example 10(b).

The obtained calcined catalyst showed poor activity and selectivity inconversion of propylene at 430° C., as seen in Table 1.

EXAMPLE 16 Preparation of Control Catalyst Co₂.0 Te₃.0 Fe₀.3 P₁.5 Mo₂₀O_(z)

A catalyst similar in composition to that of Example 10(c) above wasprepared by the hitherto known regular precipitation method, without useof a precursor stabilized by the chloride ion stabilization technique ofthe invention. The method employed was as follows:

177.0 grams of ammonium molybdate were dissolved in 600 ml water with9.5 grams of monobasic ammonium phosphate. To this solution was added:

29.1 grams of cobalt nitrate dissolved in 20 ml water;

24.0 grams of tellurium dioxide;

6.1 grams of iron nitrate dissolved in 10 ml water.

The obtained slurry was dried and calcined as in Example 10(b) above.

The calcined catalyst had poor activity and selectivity. The infraredpattern indicated the presence of mixtures of various molybdates andmetal oxides. At a temperature of 430° C. total conversion of propylenewas 48.7% at selectivities of 47.2% to acrolein and 1.7% to acrylicacid.

What is claimed:
 1. The method of converting C₃ to C₄ monoolefins to thecorresponding unsaturated carboxylic acids in a single stage operationwith accompanying production of intermediate aldehydes, which comprisescontacting such olefin at a temperature in the range of about 300° toabout 450° C. with a catalyst of the type defined as a stable activecatalyst containing a heteropoly phosphomolybdate anion in which themolybdenum is in the anion defect state obtained by a chloride ionstabilization method, which method comprises combining a molybdic acidor soluble non-metallic molybdate with a water-soluble acid ornon-metallic salt of phosphorus in aqueous solution, adding to themixture an aqueous chloride ion, optionally phosphotungstic acid or aphosphotungstate in aqueous solution and drying and calcining theresulting combination to yield a catalytically active heteropolyphosphomolybdate precursor surface, said catalyst comprising saidcatalytically active precursor surface impregnated with at least onecation from the group consisting of iron and cobalt and with a compoundcontaining a non-metallic ion selected from the group consisting oftellurium and selenium, wherein the resulting impregnated catalyst isone corresponding to an empirical formula of the group consisting of:

    M.sub.2.3-5 R.sub.2-3 P.sub.1.5-2.5 Mo.sub.20 O.sub.z

    M.sub.1-3 R.sub.0.5-2 P.sub.1-1.5 W.sub.1-2 Mo.sub.10 O.sub.z

    M.sub.1-2 R.sub.1-3 P.sub.2-4 Mo.sub.20 W.sub.1-3 O.sub.z

wherein M comprises one or more metal cations from the group consistingof iron and cobalt, R is at least one element from the group consistingof selenium and tellurium and z represents the residual valence tosatisfy the formula.
 2. The method as defined in claim 1 wherein saidimpregnated catalyst is one corresponding to the empirical formula

    Co.sub.2 Se.sub.2 Fe.sub.0.6 P.sub.1.6 Mo.sub.20 O.sub.z

wherein z represents the residual valence to satisfy the formula.
 3. Themethod as defined in claim 2 wherein said monoolefin is propylene andthe conversion products include acrylic acid and acrolein.
 4. The methodas defined in claim 1 wherein said impregnated catalyst is onecorresponding to the empirical formula

    Co.sub.2 Te.sub.3 Fe.sub.0.3 P.sub.1.6 Mo.sub.20 O.sub.z

wherein z represents the residual valence to satisfy the formula.
 5. Themethod as defined in claim 4 wherein said monoolefin is propylene andthe conversion products include acrylic acid and acrolein.